1. Field of the Invention
The present invention relates to a hydraulic damper, and more particularly to a valve structure in a hydraulic damper having telescopically interfitted inner and outer tubes, the valve structure being disposed in the inner end of the inner tube.
2. Description of the Relevant Art
There is known a telescopic hydraulic damper having an outer tube and an inner tube slidably inserted in the outer tube. A pipe member is centrally fixed at one end to the closed bottom of the outer tube which is filled with working oil, and the inner tube has an inner end positioned between the outer tube and the pipe member, with a damper valve being mounted in the inner end of the inner tube. The damper valve includes a valve body fitted over the pipe member and movable between upper and lower valve seats attached to the inner end of the inner tube. One of the valve seats is an oil locking seat which shuts off working oil between itself and the valve body when they engage each other. The other valve seat is a rebound seat which allows working oil to flow between itself and the valve body when they are brought into engagement with each other. Such a valve structure is shown in FIG. 20 of U.S. Pat. No. 4,278,266.
During the tension stroke of the damper, the valve body is held against the oil locking seat to stop the oil flow therebetween, thus producing a large damping force. During the compression stroke of the damper, especially in a high speed range, the valve body is moved off the oil locking seat into contact with the rebound seat, and the working oil flows between the vavle body and the oil locking seat and through a recess defined in the rebound seat. In the compression stroke, the damper produces a small damping force than the damping force generated during the tension stroke.
The oil locking seat has a seat surface lying perpendicularly to the longitudinal axis of the damper. The instant the valve body is unseated off the seat surface of the oil locking seat during an initial stage of the compression stroke, the working oil flow between the valve body and the oil locking seat is caused to change its direction through 90.degree.. Because of the resistance presented to the oil flow by such a sudden directional change, the damping force in the compression stroke has its peak during the initial stage thereof. There has been a demand for eliminating such a peaky damping force.